Thermocouple probes for use in gas turbine engines typically have to withstand high temperatures and high levels of vibration. At the same time, there is frequently a requirement for a long reach thermocouple, i.e. one which projects a long way into the flow duct which conveys the gas whose temperature is to be sensed, as well as a requirement for a fast response. Thus when designing an appropriate support for the thermocouple element, and an appropriate mounting arrangement for the thermocouple probe, all these factors have to be taken into account.
In gas turbine engine thermocouple probes, it is conventional to mount the thermocouple element within an outer protective sheath, to provide both strength and support. It is of course then necessary to provide some support between the thermocouple element and the protective sheath. With such an arrangement, problems caused by vibration and differential thermal expansion between the protective sheath and the thermocouple element, as well as the problem of ensuring coaxial alignment of the element within the sheath, all need to be solved, without compromising the desired fast response.
The manner in which a thermocouple probe is mounted on a gas turbine engine is critical to its survival. The Vibration levels attained in such an engine can be very high. In addition, the flow of gas through the duct may activate natural resonances in the protuberant part of the probe. Either of these factors can produce fluctuating stresses in the probe which may contribute to premature fatigue failure. It is clearly desirable to minimize such effects in an attempt to prolong the life of the probe.